1. Field of the Invention
The present invention relates to a high-voltage feedthrough capacitor for use, e.g., in a magnetron for an microwave oven for the prevention of undesired radiation noise.
2. Description of the Related Art
Various high-voltage feedthrough capacitors of this kind have been proposed and put to practical use. For example, Examined Japanese Utility Model Publication No. Hei. 7-15129 discloses a high-voltage feedthrough capacitor which employs a central conductor constituted of simple parallel flat plates wherein a longitudinally central part thereof serves as an electrode for the central conductor, and which has an electrode part facing the electrode for the central conductor and formed by processing part of a grounding plate. In this capacitor, the dielectric member disposed between the pair of electrodes is a thermosetting resin casting united with the electrodes and serving also as a filler. This dielectric member is molded by injection molding.
One problem of the conventional one described above is that since the pair of electrodes, which generate a capacitance, are constituted of a part of the grounding plate and a part of the central conductor, the area of the electrodes is influenced by the shape of the high-voltage feedthrough capacitor and cannot be increased. It has hence been difficult to secure a high capacitance by increasing the area of the electrodes and to obtain improved filter properties.
Another problem is that, if a high-permittivity material is incorporated into the thermosetting resin to be used for constituting the dielectric member between the electrodes in order to increase the permittivity of the dielectric member, the resultant thermosetting resin has impaired moldability, resulting in a reduced yield. This means that there is a limitation on obtaining an increased capacitance and thus improving filter properties, while securing moldability.
Still another problem is that since the dielectric member disposed between the electrodes serves also as a filler, it is impossible to use two resin materials having different functions in such different ways that a high-permittivity resin is used as a capacitor part and a resin having an ordinary permittivity is used as a filler. It is therefore difficult to optimize the two functions.
It is an object of the present invention to provide a high-voltage feedthrough capacitor suitable for use as a filter capacitor for preventing undesired radiation noise in a magnetron for an microwave oven.
It is another object of the present invention to provide a high-voltage feedthrough capacitor which is capable of securing a high capacitance irrespective of the shape thereof as a whole.
It is still another object of the present invention to provide a high-voltage feedthrough capacitor which has a high capacitance and is capable of improving filter properties, while securing moldability.
It is further object of the present invention to provide a high-voltage feedthrough capacitor in which resin materials having different functions can be used in such different ways that a high-permittivity resin is used as a capacitor part and a resin suitable for armoring is used as an armoring insulator.
The high-voltage feedthrough capacitor of the present invention comprises a grounding member, two feedthrough capacitors, and an armoring insulator. The grounding member has two through-holes spaced away from each other. The feedthrough capacitors each comprises one central conductor, a dielectric layer, and an electrode. The periphery of the central conductor is covered with the dielectric layer, while the surface of the dielectric layer is covered with the electrode. The feedthrough capacitors each extends through the through-hole and are fitted to the grounding member, and each electrode is bonded to the grounding member. The armoring insulator covers the peripheries of the feedthrough capacitors and the periphery of the grounding member.
In the high-voltage feedthrough capacitor of the present invention, the two feedthrough capacitors extend through the respective through-holes formed in the grounding member and are fitted to the grounding member, while the armoring insulator covers the peripheries of the feedthrough capacitors and the periphery of the grounding member. According to this structure, the high-voltage feedthrough capacitor in which both feedthrough capacitors are connected to a magnetron for an microwave oven can be used as a filter capacitor for the prevention of undesired radiation noise. In addition, the high-voltage feedthrough capacitor can have excellent electrical insulating properties and excellent moisture resistance.
In each of the feedthrough capacitors, the periphery of the central conductor is covered with the dielectric layer whose surface is covered with the electrode. The feedthrough capacitors of this structure can secure a satisfactory capacitance between each central conductor and the corresponding electrode, the capacitance being determined by the permittivity and thickness of each dielectric layer and by the area of that part of each central conductor which faces the electrode. Consequently, a high capacitance can be secured, irrespective of the shape of the high-voltage feedthrough capacitor itself, by suitably selecting those aforementioned factors in the feedthrough capacitors which govern capacitance.
The feedthrough capacitors each has been fitted to the grounding member, while the armoring insulator covers the peripheries of the feedthrough capacitors and the periphery of the grounding member. According to this structure, a material which has excellent moldability and is different from the material of the dielectric layer as a component of each feedthrough capacitor can be used to form the armoring insulator so as to cover the peripheries of the feedthrough capacitors and the periphery of the grounding member therewith. Consequently, a high capacitance can be obtained without sacrificing moldability, whereby a high-voltage feedthrough capacitor having excellent filter properties can be obtained.
Furthermore, since the dielectric layer of each feedthrough capacitor and the armoring insulator are separate components, materials having different functions can be used in such different ways that a resin having high permittivity is used as the dielectric layer of each feedthrough capacitor and a resin suitable for armoring is used as the armoring insulator.